Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

[David Rientjes <rientjes@google.com>]

On Tue, 25 Oct 2011, Mel Gorman wrote:

> That said, it will be difficult to remember why checking __GFP_NOFAIL in
> this case is necessary and someone might "optimitise" it away later. It
> would be preferable if it was self-documenting. Maybe something like
> this? (This is totally untested)
> 

__GFP_NOFAIL _should_ be optimized away in this case because all he's 
passing is __GFP_WAIT | __GFP_NOFAIL.  That doesn't make any sense unless 
all you want to do is livelock.

__GFP_NOFAIL doesn't mean the page allocator would infinitely loop in all 
conditions.  That's why GFP_ATOMIC | __GFP_NOFAIL actually fails, and I 
would argue that __GFP_WAIT | __GFP_NOFAIL should fail as well since it's 
the exact same condition except doesn't have access to the extra memory 
reserves.

Suspend needs to either set __GFP_NORETRY to avoid the livelock if it's 
going to disable all means of memory reclaiming or freeing in the page 
allocator.  Or, better yet, just make it GFP_NOWAIT.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>